The active matrix flat panel display, such as the liquid crystal display utilizes the Thin Film Transistor (TFT) elements to be the driving elements. Generally, the inorganic semiconductor material has higher mobility, and thus has been widely employed to be the semiconductor layer material of the thin film transistor. In comparison with the inorganic semiconductor material, the organic semiconductor material has lower mobility but possesses being light and thin, flexible and the adaptability of low temperature manufacture process. Therefore, the organic semiconductor material has been used for experiment to manufacture the thin film transistor elements in the industry, recently.
At present, most of the organic semiconductor material is the P type material. For making the better ohm contact of the metal and the organic semiconductor material, the material with larger work function, such as gold (Au), silver (Au), aluminum (Al), Indium Tin Oxide (ITO) is selected to be the material of the source, drain electrodes to reduce the Schottky barrier of interface of the metal and the semiconductor. It is more beneficial for the injection of the carriers, and thus is effectively to reduce the contact resistance. The usage cost of Au is higher. Therefore, the practical application is less. The metals, such as Ag, Al is easily oxidized and corroded by the following processes, such as the influence of the plasma etching, and accordingly, the connection with the pixel electrode is influenced. The ITO is commonly employed to be the transparent pixel electrode material and has excellent electrical properties, and the work function is higher, and is hardly to be oxidized. Thus, it has been widely applied for being the anode material of the organic light emitting diode (OLED). However, the resistance is larger, therefore it has restriction in the development and application of the organic thin film transistor elements and the array substrate thereof.